Credit where it's due - I'm not normally a Daily Mail fan (though did you know they have the world's number 1 most visited news website?), but when my Mum showed me this in their Live magazine, it was the first I'd heard of it.
Here's the picture (click on it for a closer look) and the Daily Mail article does a good job of explaining it, so click on that for the full story.
I've got form with maps on musical themes - a few years ago there was a Tube map created with each line a musical genre, and all the stations different artists, so the intersections were artists who straddled the appropriate genres. I bought it, framed it and stuck it on my wall. I would show you a photo but it's currently being re-framed after my removal guy to Denmark had an unfortunate coming together with a bridge in France. Anyway, that's another story...
You can buy the poster from the creators, an agency called Dorothy. I'd very much recommend you do because it'll look lovely next to your musical Tube map. Or is that just me?